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>>                                                      CERT-NL, 01-Mar-2000 <<
>> All CERT-NL information has been moved to http://cert.surfnet.nl.  Links  <<
>> to CERT-NL information contained in this advisory are therefore outdated. <<
>>                                                                           <<
>> CERT-NL also has stopped the CERT-CC-Mirror service.  Due to this the     <<
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Security Advisory                                                       CERT-NL
===============================================================================
Author/Source : Don Stikvoort                               Index  :    S-97-40
Distribution  : World                                       Page   :          1
Classification: External                                    Version:          1
Subject       : SGI IRIX df Buffer Overrun Vulnerability    Date   :  30-May-97
===============================================================================

By courtesy of AUSCERT we received
information on an SGI IRIX df Buffer Overrun vulnerability.

This can lead to root compromises.

CERT-NL recommends taking action 3.1 mentioned below and wait for the
official SGI patches. SGI acknowledged this problem on May 28th:

<QUOTE>
Silicon Graphics Inc. acknowledges the df buffer overrun vulnerability
publically reported by several individuals and in AUSCERT Advisory AA-97.19.

Currently, Silicon Graphics Inc. is investigating and no further information
is available for public release at this time.

As further information becomes available, additional advisories will be
issued via the normal SGI security information distribution methods
including the wiretap mailing list.
<UNQUOTE>

==============================================================================

AA-97.19                        AUSCERT Advisory
                    SGI IRIX df Buffer Overrun Vulnerability
                                 26 May 1997

Last Revised:   --

  ---------------------------------------------------------------------------

AUSCERT has received information that a vulnerability exists in df(1),
distributed under IRIX 5.3, 6.2 and 6.3.  Other versions may also be
vulnerable.

This vulnerability may allow local users to gain root privileges.

Exploit information involving this vulnerability has been made publicly
available.

At this stage, AUSCERT is unaware of any official vendor patches.  AUSCERT
recommends that sites apply the workaround given in Section 3 until vendor
patches are made available.

This advisory will be updated as more information becomes available.

  ---------------------------------------------------------------------------

1.  Description

    df(1) is a program used to display statistics about the amount of used
    and free disc space on file systems.

    Due to insufficient bounds checking on arguments which are supplied
    by users, it is possible to overwrite the internal stack space of the
    df program while it is executing.  By supplying a carefully designed
    argument to the df program, intruders may be able to force df to
    execute arbitrary commands.  As df is setuid root, this may allow
    intruders to run arbitrary commands with root privileges.

    Sites can determine if this program is installed by using:

  % ls -l /sbin/df

    df is installed by default in /sbin.  Sites are encouraged to check
    for the presence of this program regardless of the version of IRIX
    installed.

    Exploit information involving this vulnerability has been made publicly
    available.

2.  Impact

    Local users may gain root privileges.

3.  Workarounds/Solution

    AUSCERT recommends that sites prevent the exploitation of this
    vulnerability in df by immediately applying the workaround given in
    Section 3.1.

    If the df functionality is required by non-root users, AUSCERT recommends
    applying the workaround given in Section 3.2.

    Currently there are no vendor patches available that address this
    vulnerability.  AUSCERT recommends that official vendor patches be
    installed when they are made available.

3.1 Remove setuid and non-root execute permissions

    To prevent the exploitation of the vulnerability described in this
    advisory, AUSCERT recommends that the setuid permissions be removed
    from the df program immediately.  As df will no longer work for non-root
    users, it is recommended that the execute permissions for them also
    be removed.

  # ls -l /sbin/df
  -r-sr-xr-x   1 root   sys     23136 Nov 22  1994 /sbin/df

  # chmod 500 /sbin/df
  # ls -l /sbin/df
        -r-x------   1 root   sys     23136 Nov 22  1994 /sbin/df

3.2 Install df wrapper

    AUSCERT has developed a wrapper to help prevent programs from being
    exploited using the vulnerability described in this advisory.  Sites
    which have a C compiler can obtain the source, compile and install
    the wrapper as described in Section 3.2.1.  For sites without a C
    compiler, AUSCERT has made pre-compiled binaries available
    (Section 3.1.2).

3.2.1 Installing the wrapper from source

    The source for the wrapper, including installation instructions, can
    be found at:

        ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/
                                               overflow_wrapper.c

    This wrapper replaces the df program and checks the length of the
    command line arguments which are passed to it.  If an argument exceeds
    a certain predefined value (MAXARGLEN), the wrapper exits without
    executing the df command.  The wrapper program can also be configured
    to syslog any failed attempts to execute df with arguments exceeding
    MAXARGLEN.  For further instructions on using this wrapper, please
    read the comments at the top of overflow_wrapper.c.

    When compiling overflow_wrapper.c for use with df, AUSCERT recommends
    defining MAXARGLEN to be 32.

    The MD5 checksum for the current version of overflow_wrapper.c can be
    retrieved from:

        ftp://ftp.auscert.org.au/pub/auscert/tools/overflow_wrapper/CHECKSUM

    The CHECKSUM file has been digitally signed using the AUSCERT PGP key.

3.2.2 Installing the wrapper binaries

    Pre-compiled wrapper binary is provided for sites that wish to install
    the wrapper but do not have a C compiler available.  AUSCERT has
    compiled the wrapper on IRIX 5.3, however later versions of IRIX should
    be able to use the wrapper binary without recompilation.  The following
    compile time options have been used to create the binaries:

        REAL_PROG='"/sbin/df.real"'
        MAXARGLEN=32
        SYSLOG

    More information on these options can be found in Section 3.1.1 and
    in the overflow_wrapper.c source code.

    The pre-compiled binaries for the wrapper program can be retrieved from:

  ftp://ftp.auscert.org.au/pub/auscert/tools/AA-97.19-df_wrapper.tar.Z

    The MD5 checksum for AA-97.19-df_wrapper.tar.Z is:

        MD5 (AA-97.19-df_wrapper.tar.Z) = 9d21e6358129cccbe3768757a5361f56

    AA-97.19-df_wrapper.tar.Z contains a README file with installation
    instructions, as well as a pre-compiled binary.

    Sites are encouraged to carefully read the installation notes in the
    README file before installation.

==============================================================================
CERT-NL is the Computer Emergency Response Team for SURFnet customers. SURFnet
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===============================================================================

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